Serious engine troubles

[hypophthalmus]

Yes. Still tightened down too.

[CROSSBOLT]

Look carefully at the cam lobes. Are they smooth and shiny?

Karl

[hypophthalmus]

Yes, normally so.

[gregspeople250]

Cool radiator when engine is hot = VERY BAD NEWS. No or little coolant in the system. Kaput!
Hopefully, this isn't the case.

[hypophthalmus]

I'm not sure. Besides the heat suddenly spiking, there hasn't been any cooling issues. And I don't have reason to suspect I've been losing coolant. I can check though.

The sides of the radiator were definitely warmer than the fins. I was thinking maybe there was momentarily bad circulation from some air (once I got it started again, the gauge plunged back to the middle of the range). Or maybe all the airflow was just cooling off the radiator effectively? I don't remember how it normally is.

[Stig / Major Tom]

Regardless of what was, or was not,  going on previously with the radiator....."the very bad noise heard 2nd time engine stopped" seems to warrant opening the engine further. ?remove cylinder head?
Show parts to forum or scooter shop to get ideas of causes, possibility of repairs, etc.
600 high speed miles on a 10 yr old 250 .....oil lubricity or coolant system failure, valve settings, spark plug heat range,  cam chain, come to my mind.
Hang in there,
Stig

[ole two wheels]

All the pencil deal is good for is to tell you if the piston is still moving up and down. No piston movement = broken rod. Whatever caused the heat to spike could result in a broken rod. Once an engine gets hot enough, the piston can no longer slide in the cylinder and something has to give. I hope this is not the case. The pencil trick is just a quick and simple way to tell for sure without taking the engine apart. Since I'm the only one who thinks that's a possibility, I'll let this be my final comments. I wish you luck on finding the problem.

[hypophthalmus]

There's a lot more than 600 high speed miles on it. That's just how many high speed miles without incident since I accidentally left the clamp loose on the coolant hose for a few seconds.

But yes, engine disassembly seems to be in order.

Ole two wheels,

I think some miscommunication happened. I agree that a broken rod is a definite possibility, and I'm glad you mentioned it since it wouldn't have occurred to me. Although I hope that's not it, since it looks like I would need an entire new crankshaft, which are apparently quite expensive and presumably difficult to replace.

I understand the trick, but my engine seized before I could be sure if I felt the piston move. Once I get the head off, I'll be able to see it though.

[CROSSBOLT]

All of us are standing by to hear what you find. To help as best we can.

Karl

[hypophthalmus]

Thanks, I appreciate it!

It'll probably be slow going, with limited time and a sprained wrist (from pushing the bike up a uhaul ramp I think, even with a helpful stranger's assistance).

Draining the coolant was the first thing to do anyways. It was low, although not as much as it seemed.

I weighed what came out, and it works out to about 0.9 liters, when it's supposed to be 1.0 liters. It didn't come up to the neck. The reserve tank was also significantly lower than last I checked, and it had been stable for a long time before.

[hypophthalmus]

Also, having changed the head gasket on my van last summer, I'm appreciating how accessible everything is in comparison. And the incredible number of things I don't need to remove first.

A question: the manual is telling me to set the engine to top dead center before taking off the camshaft. Is there a reason why, and can I safely ignore that?

[CROSSBOLT]

TDC on compression stroke makes it easier to put everything back in time.

Karl

[Mr. Paul]

I cant add much help here, but I'm pulling for ya Hypothalmus!

[Redk]

Karl is correct, of course, yet at this point, It's not gonna make a difference.
Most likely a complete engine tear-down will be required.
My question is, what is the quickest way to remove the engine unit from the scooter ?
redk

Oh, and sry to hear of failure, but this is what does happen to machines, eventually.
My guess is it will be far less expensive to get back into working condition than many other brands.

[hypophthalmus]

Thanks, Paul!

I didn't think the engine position would matter, but I didn't want to be surprised with something.

I'm going to try not to remove the engine if I can avoid it. But the engine/transmission/wheel should unbolt from the frame as one unit pretty easily I think.

I feel like it's too low miles and I've put too much care into it for it to be a reasonable fate. That combined with the suddenness is disconcerting when I want to be able to safely drive into the middle of nowhere, and expect to be able to get back.

As far as less expensive, I'm not sure. More common bikes might benefit from more used parts. And i've noticed that small Kymco parts (nuts, bushings, etc) are frequently more expensive. A quick search for instance shows used Silverwing and various V-Star crankshafts in good condition for significantly less. And it seems that you can buy V Star piston rods separately, which is much much cheaper.